Recently, in line with miniaturization, lightweight, thin profile, and portable trends in electronic devices according to the development of information and telecommunications industry, the need for high energy density batteries used as power sources of such electronic devices has increased. Currently, research into lithium secondary batteries, as batteries that may best satisfy the above need, has actively conducted.
Various types of carbon-based materials including artificial graphite, natural graphite, or hard carbon, which are capable of intercalating/deintercalating lithium, have been used as anode active materials of lithium secondary batteries. Among the carbon-based materials, since graphite provides advantages in terms of energy density of a lithium secondary battery and also guarantees long lifespan of the lithium secondary battery due to excellent reversibility, graphite has been most widely used.
However, since graphite may have a low capacity in terms of energy density per unit volume of an electrode and may facilitate side reactions with an organic electrolyte at a high discharge voltage, there is a risk of fire or explosion due to malfunction and overcharge of the battery.
Thus, metal-based anode active materials, such as silicon (Si), have been studied. It is known that a silicon-based anode active material exhibits high capacity. However, the silicon-based anode active material may cause a maximum volume change of 300% or more before and after the reaction with lithium, i.e., during charge and discharge. As a result, conductive networks in the electrode may be damaged and contact resistance between particles may be increased to degrade lifetime characteristics of the battery.
In addition, a thick non-conductive side reaction product layer may be formed on the surface of the silicon-based anode active material during charge and discharge due to the continuous reaction with an electrolyte solution. As a result, the silicon-based anode active material may be electrically short-circuited in the electrode to degrade the lifetime characteristics.
Therefore, there is a need to develop an anode active material which may replace a typical anode active material and may improve the lifetime characteristics and effect of reducing volume expansion of a lithium secondary battery due to less reaction with the electrolyte solution when used in the lithium secondary battery.